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[84.3.50.134]) by smtp.gmail.com with ESMTPSA id p19sm2793453edr.57.2021.03.25.07.18.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 25 Mar 2021 07:18:28 -0700 (PDT) Sender: Ingo Molnar Date: Thu, 25 Mar 2021 15:18:20 +0100 From: Ingo Molnar To: Dmitry Vyukov Cc: Marco Elver , Peter Zijlstra , Alexander Shishkin , Arnaldo Carvalho de Melo , Ingo Molnar , Jiri Olsa , Mark Rutland , Namhyung Kim , Thomas Gleixner , Alexander Potapenko , Al Viro , Arnd Bergmann , Christian Brauner , Jann Horn , Jens Axboe , Matt Morehouse , Peter Collingbourne , Ian Rogers , kasan-dev , linux-arch , linux-fsdevel , LKML , the arch/x86 maintainers , "open list:KERNEL SELFTEST FRAMEWORK" Subject: Re: [PATCH v3 07/11] perf: Add breakpoint information to siginfo on SIGTRAP Message-ID: <20210325141820.GA1456211@gmail.com> References: <20210324112503.623833-1-elver@google.com> <20210324112503.623833-8-elver@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org * Dmitry Vyukov wrote: > On Wed, Mar 24, 2021 at 3:05 PM Marco Elver wrote: > > > > On Wed, 24 Mar 2021 at 15:01, Peter Zijlstra wrote: > > > > > > One last try, I'll leave it alone now, I promise :-) > > > > This looks like it does what you suggested, thanks! :-) > > > > I'll still need to think about it, because of the potential problem > > with modify-signal-races and what the user's synchronization story > > would look like then. > > I agree that this looks inherently racy. The attr can't be allocated > on stack, user synchronization may be tricky and expensive. The API > may provoke bugs and some users may not even realize the race problem. Yeah, so why cannot we allocate enough space from the signal handler user-space stack and put the attr there, and point to it from sig_info? The idea would be to create a stable, per-signal snapshot of whatever the perf_attr state is at the moment the event happens and the signal is generated - which is roughly what user-space wants, right? Thanks, Ingo